The present invention relates to a gas flow type angular velocity sensor which is capable of electrically sensing a deflection of a gas flow, which is caused by the action of an angular velocity applied to the sensor body.
Japanese laid open patent publication No. 4623/89 describes such a gas flow type angular velocity sensor in which gas is forced into a gas path in the sensor body through a nozzle hole to flow therealong toward a pair of heat wires, each being composed of a thermo-sensitive resistance element. When an angular velocity is applied to the sensor body, the gas flow is deflected and, accordingly, a difference between thermosensitive outputs of two heat wires is produced and picked up for determining therefrom a direction and a magnitude of the angular velocity acting on the sensor body.
Since the above-mentioned angular velocity sensor is designed to determine an angular velocity by sensing a very small differential change of heat radiation of two heat wires (i.e., thermosensitive resistances), temperature variation of the gas flow may affect the detecting accuracy of the sensor. For this reason, the conventional gas flow type sensor is mounted in a fixed temperature case capable of keeping temperature therein at a constant level to avoid the effect of ambient temperature variations.
Recently, there has been also developed a gas rate sensor of the type that has its body portion composed of a gas path and the pair of heat wires therein are manufactured by semiconductor micro-machining on the basis of IC technology. This is disclosed in Japanese laid open patent publication No. 29858/92.
However, in contrast to a conventional gas rate sensor having a gas path of relatively large volume to absorb pulsation and fluctuation of the gas flow produced by a pump that alternately sucks and exhausts gas, a gas rate sensor having a gas path of relatively small volume can not absorb the above-mentioned pulsation or fluctuation of the gas flow, which appears as a noise component in the sensor's output. This results in lowering the accuracy of angular velocity measurement.
The above-mentioned prior art devices have the following problems to be solved:
1) The first problem is that the fixed temperature case containing a sensor body requires the provision of heating means of relatively large output power so as to evenly heat up the inner space of the fixed temperature case. It also takes time to heat up the fixed temperature case until its inside temperature rises to a constant level, at which the sensor can accurately measure an angular velocity. Furthermore, the response of the fixed temperature case temperature control is somewhat insufficient to prevent the possible effects of ambient temperature variations.
2) The second problem arising in using a small-sized sensor having a reduced volume of a gas path is that pulsing gas flows created by pumping operations can not be absorbed in the normal gas path and produce noise components which may be induced into outputs of the sensor.